1. Field of the Invention
The present invention relates to a demodulation apparatus and a demodulation method for mobile communication. In particular, it relates to a demodulation apparatus and a demodulation method for mobile communication adopting CDMA (Code Division Multiple Access).
2. Description of the Related Art
Conventionally, in a demodulation circuit as mentioned above a path diversity effect is obtained by path search and RAKE combining. Examples in the prior art of this kind are disclosed in Japanese Patent Laid-Open No. 10-94041 (hereafter referred to as document 1), Japanese Patent Laid-Open No. 10-200506 (hereafter referred to as document 2), Japanese Patent Laid-Open No. 11-251962 (hereafter referred to as document 3), and Japanese Patent Laid-Open No. 11-261528 (hereafter referred to as document 4).
The technique disclosed in document 1 involves using at least one of the receiving fingers for search. The technique disclosed in document 2 involves saving the maximum value among previous correlation values and using the maximum value in selecting high values out of correlation values. The technique disclosed in document 3 involves detecting reception levels from reception signals, to compare them with a predetermined threshold, and to determine whether or not a correlation signal of an internal memory should be outputted to a reception path timing generation section depending on the comparison result. The technique disclosed in the document 4 involves reading a sequence of measurements, deriving a timing offset having a resolution higher than a predetermined timing resolution of a searcher unit, and assigning a finger processing element to the best candidate path using the timing offset.
In a mobile communication environment, radio waves to be received are suffered from changes including appearance and disappearance caused by shadowing. Paths that have not been path-searched in intense path changes become interfering components for a receiver and degrade the reception characteristics. Thus, path search with high accuracy and high speed is desired. However, none of the above mentioned documents from 1 to 4 describe measures for solving this problem.